New Global Tectonics

(also plate tectonics), a tectonic hypothesis that is a modern variation of the drift theory, or mobilism. It was formulated as a complete concept in 1968 by W. J. Morgan, X. LePichon, B. Isacks, J. Oliver, L. Sykes, and others, who elaborated the ideas of the American geologists R. S. Dietz and H. H. Hess concerning sea-floor spreading. However, its basic principles were outlined in 1929 by the Scottish geologist A. Holmes, who incorporated O. Ampferer’s hypothesis of subscrustal currents, J. Joly’s radiogenic hypothesis, and A. Wegener’s continental drift hypothesis.

According to the new global tectonics, the lithosphere, which rests on the less viscous asthenosphere, is divided into a number of plates. The boundaries of these plates are zones of maximum tectonic, seismic, and volcanic activity. It is along these boundaries that the plates move apart, thrust over, thrust under, and are displaced horizontally relative to each other. In the rift zones of the midocean ridges, the plates move apart and the openings fill with basaltic magma welling up from the asthenosphere. Convection currents in the asthenosphere carry the plates laterally away from the axis of the midocean ridges. Along the island arcs and continental margins the plates of the oceanic crust are thrust under the continental crust and a thickening of the continental crust accompanies compression, discharge of heat, and the rise of silica, alkalies, and water vapors, resulting in andesitic volcanism, granitization, folding, and regional metamorphism.

Supported by new, geological and geophysical facts obtained during the last few decades, particularly facts regarding the oceans, the concept of the new global tectonics has gained considerable popularity. However, it has also encountered serious objections concerning the mechanism of convection, the subduction of the oceanic crust beneath the continents, and other issues (V. V. Belousov, Iu. M. Sheinman, E. V. Artiushkov). Numerous investigators reject the concept completely.